Sod harvesting machines have been commercially available for a long time and are generally designed as a self-propelled machine or as a cutting unit which can be attached to a conventional tractor. The cutting head includes (a) a generally-horizontal knife to undercut the sod at a specified depth, and (b) side cutting blades at opposite ends of the horizontal knife to cut the edges of a sod strip. A roller can be included forwardly of the knife on a horizontal axis to support the weight of the cutting head and establish the thickness of the sod strip.
One problem with conventional sod harvesters or sod cutting heads which are rigidly mounted to the tractor or driving implement is that the cutting head does not follow the contour of the ground closely enough to assure that the cut sod strip will be of a uniform thickness from side-to-side as the harvester moves across the field.
An improved sod harvester is described in U.S. Pat. No. 4,621,696 in which a sod cutting head is pivotally mounted to a fixed frame by a horizontal front pivot shaft and by a pair of rear pivots. As the gage roller tilts to the left or to the right when following the contour of the ground, the cutting knife and side rollers or knives must also swing to the left or to the right by a distance proportional to the degree of rotation and the normal distance from the lower edge of the gage roller to the axis of rotation of the cutting head. Such sideways movement is usually prevented because of the side restraining effect of the side rollers or knives and the short distance between undulations. The result is that the sod strip tends to vary in thickness across its width, sometimes to the extent that the strip is less than zero in thickness on one side. Extreme variation in thickness across the width of the sod strip is referred to as "scalping".
There has not heretofore been provided a sod harvesting apparatus which effectively minimizes the problem of non-uniform sod cutting.